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Cross-Modal Calibration of Vestibular Afference for Human Balance.

Héroux ME, Law TC, Fitzpatrick RC, Blouin JS - PLoS ONE (2015)

Bottom Line: In effect, this changed vestibular afferent gain.Reflex muscle responses evoked by an independent, higher bandwidth vestibular stimulus were initially reduced in amplitude by the galvanic stimulus but returned to normal levels after the conditioning period, contrary to predictions that they would decrease after adaptation to increased sensory gain and increase after adaptation to decreased sensory gain.This result is inconsistent with sensory reweighting based on disturbances.

View Article: PubMed Central - PubMed

Affiliation: School of Kinesiology, University of British Columbia, Vancouver, Canada.

ABSTRACT
To determine how the vestibular sense controls balance, we used instantaneous head angular velocity to drive a galvanic vestibular stimulus so that afference would signal that head movement was faster or slower than actual. In effect, this changed vestibular afferent gain. This increased sway 4-fold when subjects (N = 8) stood without vision. However, after a 240 s conditioning period with stable balance achieved through reliable visual or somatosensory cues, sway returned to normal. An equivalent galvanic stimulus unrelated to sway (not driven by head motion) was equally destabilising but in this situation the conditioning period of stable balance did not reduce sway. Reflex muscle responses evoked by an independent, higher bandwidth vestibular stimulus were initially reduced in amplitude by the galvanic stimulus but returned to normal levels after the conditioning period, contrary to predictions that they would decrease after adaptation to increased sensory gain and increase after adaptation to decreased sensory gain. We conclude that an erroneous vestibular signal of head motion during standing has profound effects on balance control. If it is unrelated to current head motion, the CNS has no immediate mechanism of ignoring the vestibular signal to reduce its influence on destabilising balance. This result is inconsistent with sensory reweighting based on disturbances. The increase in sway with increased sensory gain is also inconsistent with a simple feedback model of vestibular reflex action. Thus, we propose that recalibration of a forward sensory model best explains the reinterpretation of an altered reafferent signal of head motion during stable balance.

No MeSH data available.


Vestibular reflex responses to galvanic stimuli.(A) For a typical subject, responses in right tensor fascia lata muscle (TFL) muscle measured as cumulant density to stochastic galvanic stimulation are shown for each GVS modulation stimulus, before (gray) and after (black) visual conditioning. The biphasic short-latency (~50ms) and long-latency responses are evident. (B) Group mean of peak medium latency response amplitude with 95% CIs in medial gastrocnemius (MG) and TFL. * P < 0.05.
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pone.0124532.g004: Vestibular reflex responses to galvanic stimuli.(A) For a typical subject, responses in right tensor fascia lata muscle (TFL) muscle measured as cumulant density to stochastic galvanic stimulation are shown for each GVS modulation stimulus, before (gray) and after (black) visual conditioning. The biphasic short-latency (~50ms) and long-latency responses are evident. (B) Group mean of peak medium latency response amplitude with 95% CIs in medial gastrocnemius (MG) and TFL. * P < 0.05.

Mentions: Typical EMG responses evoked by the stochastic vestibular stimulus in the right TFL muscle are shown in Fig 4A. This stochastic stimulus used to identify the response in vestibular reflex pathways is unrelated to the sway modulated stimuli being examined. Without a sway-modulated stimulus, robust biphasic reflex responses were seen with a short-latency response at ~50 ms and a medium-latency response at ~100 ms. Similar responses were observed in both muscles (TFL, MG) bilaterally. Both the sway-modulated stimulus and the non-coherent stimulus markedly reduced the short- and medium-latency vestibular reflex responses compared with the no-stimulus trials (compare gray plots). After visual conditioning of the sway-modulated stimuli, the responses increased in amplitude to approach the levels of the no-stimulus control (black lines). This was not seen with the visual conditioning of the non-coherent stimulus.


Cross-Modal Calibration of Vestibular Afference for Human Balance.

Héroux ME, Law TC, Fitzpatrick RC, Blouin JS - PLoS ONE (2015)

Vestibular reflex responses to galvanic stimuli.(A) For a typical subject, responses in right tensor fascia lata muscle (TFL) muscle measured as cumulant density to stochastic galvanic stimulation are shown for each GVS modulation stimulus, before (gray) and after (black) visual conditioning. The biphasic short-latency (~50ms) and long-latency responses are evident. (B) Group mean of peak medium latency response amplitude with 95% CIs in medial gastrocnemius (MG) and TFL. * P < 0.05.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4403994&req=5

pone.0124532.g004: Vestibular reflex responses to galvanic stimuli.(A) For a typical subject, responses in right tensor fascia lata muscle (TFL) muscle measured as cumulant density to stochastic galvanic stimulation are shown for each GVS modulation stimulus, before (gray) and after (black) visual conditioning. The biphasic short-latency (~50ms) and long-latency responses are evident. (B) Group mean of peak medium latency response amplitude with 95% CIs in medial gastrocnemius (MG) and TFL. * P < 0.05.
Mentions: Typical EMG responses evoked by the stochastic vestibular stimulus in the right TFL muscle are shown in Fig 4A. This stochastic stimulus used to identify the response in vestibular reflex pathways is unrelated to the sway modulated stimuli being examined. Without a sway-modulated stimulus, robust biphasic reflex responses were seen with a short-latency response at ~50 ms and a medium-latency response at ~100 ms. Similar responses were observed in both muscles (TFL, MG) bilaterally. Both the sway-modulated stimulus and the non-coherent stimulus markedly reduced the short- and medium-latency vestibular reflex responses compared with the no-stimulus trials (compare gray plots). After visual conditioning of the sway-modulated stimuli, the responses increased in amplitude to approach the levels of the no-stimulus control (black lines). This was not seen with the visual conditioning of the non-coherent stimulus.

Bottom Line: In effect, this changed vestibular afferent gain.Reflex muscle responses evoked by an independent, higher bandwidth vestibular stimulus were initially reduced in amplitude by the galvanic stimulus but returned to normal levels after the conditioning period, contrary to predictions that they would decrease after adaptation to increased sensory gain and increase after adaptation to decreased sensory gain.This result is inconsistent with sensory reweighting based on disturbances.

View Article: PubMed Central - PubMed

Affiliation: School of Kinesiology, University of British Columbia, Vancouver, Canada.

ABSTRACT
To determine how the vestibular sense controls balance, we used instantaneous head angular velocity to drive a galvanic vestibular stimulus so that afference would signal that head movement was faster or slower than actual. In effect, this changed vestibular afferent gain. This increased sway 4-fold when subjects (N = 8) stood without vision. However, after a 240 s conditioning period with stable balance achieved through reliable visual or somatosensory cues, sway returned to normal. An equivalent galvanic stimulus unrelated to sway (not driven by head motion) was equally destabilising but in this situation the conditioning period of stable balance did not reduce sway. Reflex muscle responses evoked by an independent, higher bandwidth vestibular stimulus were initially reduced in amplitude by the galvanic stimulus but returned to normal levels after the conditioning period, contrary to predictions that they would decrease after adaptation to increased sensory gain and increase after adaptation to decreased sensory gain. We conclude that an erroneous vestibular signal of head motion during standing has profound effects on balance control. If it is unrelated to current head motion, the CNS has no immediate mechanism of ignoring the vestibular signal to reduce its influence on destabilising balance. This result is inconsistent with sensory reweighting based on disturbances. The increase in sway with increased sensory gain is also inconsistent with a simple feedback model of vestibular reflex action. Thus, we propose that recalibration of a forward sensory model best explains the reinterpretation of an altered reafferent signal of head motion during stable balance.

No MeSH data available.